The present invention relates to a method for the removal of first molecules that are adsorbed upon the surfaces of a chamber and/or of at least one object located in the chamber, in particular to the removal of polar molecules from a processing or transfer chamber of a rapid heating unit.
With many methods carried out within a processing chamber, such as, for example, CVD processes or thermal treatments of objects, especially in the semiconductor industry and microelectronics, moisture can, for example, adversely affect the process. Moisture tends to become adsorbed on the chamber walls, the objects, such as, for example, semiconductor substrates, or other elements in the chamber. Examples of processes that are adversely affected by the presence of water are the production of ultra shallow pn-junctions (ultra shallow junctions), metalizing or coating processes, and many CVD processes. In addition, water adversely affects so-called COP""s or crystal originated particles, as well as the formation of oxygen-free surface layers (magic denuded zones).
The water molecules adsorbed on the chamber walls or on the substrates lead to undesired chemical reactions that adversely affect a treatment result. Primarily during the thermal treatment of semiconductor substrates, water negatively acts within the reaction chamber upon the substrates that are to be treated or upon the layers applied thereon. For example, water in the order of magnitude of less than 1 ppm to several 100 ppm in an oxygen-free atmosphere has an etching effect, as a function of the process temperature, upon silicon or GaAs wafers during a thermal treatment. An originally smoothly polished surface of the wafer is thereby atomically roughened. It is possible for zones of a diffused haze to form upon the wafer. Structures provided on the substrate surface can be destroyed or at least adversely affected thereby. Furthermore, the material of the semiconductor wafer that has been etched away could be deposited at some other location within the processing chamber, thereby contaminating the chamber.
The cause for water within a processing chamber is primarily the humidity of the atmospheric air. With every opening of the processing chamber, for example for the removal and introduction of the object that is to be treated or during maintenance work, air enters the processing chamber. In clean rooms, the relative humidity is generally between 38% and 42%. The water present in the air is deposited upon the object to be treated or the inner chamber walls. This problem occurs particularly intensely after a previously effected wet chemical treatment of the object. In such cases, water is adsorbed in substantially greater quantities by the substrate surface However, also special coatings of a wafer with various materials, as frequently occurs in the semiconductor industry, can increase the adsorption effect relative to water. Silicon dioxide, which is frequently used as a coating material, is extremely hydrophilic and has a large adsorption effect relative to water. In particular during CVD processes, the processing chamber can become contaminated by pulverous deposits. In these cases, a large quantity of water can be absorbed, since as a consequence of the pulverous micro particles in the chamber, an increased surface results for the adsorption.
To remove water from a processing chamber, it is known to rinse the chamber with an inert gas over a long period of time. In this connection, rinsing times of up to 12 hours are not at all uncommon in order to reduce the water content within the processing chamber to an acceptable level, as is described, for example, by Andrew, Inman, Haider, Gillespie and Brookshire in xe2x80x9cIncreasing equipment uptime through in situ moisture monitoringxe2x80x9d, Solid State Technology, August 1998. With systems where the substrate is introduced into the chamber via a transfer mechanism, so-called load-lock-systems, it is not necessary to rinse the entire chamber, but rather merely the smaller transfer chamber in which the wafer is located prior to the loading. Although the rinsing time is thereby reduced to 4 hours, it is still extremely long, as a result of which the treatment of semiconductor wafers becomes uneconomical.
Proceeding from this known method, it is therefore an object of the present invention to provide a method for the rapid and efficient removal of polar molecules, such as, for example, water molecules, but also non-polar molecules, such as, for example, oxygen molecules, from a chamber. In this connection, the present invention is related in particular to the removal of water molecules from a processing and/or transfer chamber of a rapid heating unit.
Pursuant to the present invention, the object is realized by introducing second polar molecules into the chamber that exert a desorptive effect upon the first molecules. The introduction of the second polar molecules accelerates the desorption of the undesired first molecules. After detaching the first molecules, the second polar molecules preferably assume the location of the first molecules, thus preventing a renewed adsorption. As a consequence, more rapidly prescribed threshold values can be achieved for the concentration of the first molecules within the chamber, as a result of which the throughput rates of the unit, and hence its economy, can be increased. At the same time, lower values of the concentration of the first molecules can be achieved within the chamber, which leads to improved process results. The first molecules are preferably water and/or oxygen molecules that can have an etching effect upon the semiconductor wafer. By removing these molecules, damage to the wafers or the structures provided thereon can therefore be prevented. Pursuant to one preferred embodiment of the invention, prior to, during and/or after the introduction of the second polar molecules, a rinsing gas, especially an inert gas or N2, is conveyed through the chamber in order to reliably take the desorbed first molecules out of the chamber. In this connection, according to one embodiment of the invention initially rinsing gas and subsequently a mixture of rinsing gas and the second polar molecules are preferably conveyed through the chamber in order to initially achieve a preliminary rinsing. Only after the preliminary rinsing are the second polar molecules conveyed through the chamber in order to effect a further desorption of the first molecules. As a result of this two-stage step, the quantity of the second polar molecules utilized can be reduced. In order to take, for example, water away at a relative humidity of about 40% and at room temperature by means of NH3, a mixture ratio of 9:1 between the rinsing gas and the polar NH3 has been shown to be advantageous.
Pursuant to an alternative embodiment, first the rinsing gas and subsequently the second polar molecules are conveyed through the chamber in order to again achieve a two-stage process. Due to the fact that in the second stage only polar molecules are conveyed through the chamber, the desorptive effect is significantly increased. After the second step, a rinsing gas can again be advantageously conveyed through the chamber.
To promote the desorption of the first molecules, the temperature within the chamber is preferably controlled. In this connection, the walls of the chamber and/or an object found in the chamber, such as, for example, a semiconductor wafer, are preferably heated. For a good desorption effect, the object is preferably heated to a temperature range between 400xc2x0 C. and 800xc2x0 C.
The desorption can advantageously also be enhanced by heating the second polar molecules and/or the rinsing gas prior to the introduction into the chamber.
Pursuant to one preferred embodiment of the invention, the second polar molecules comprise nitrogen and hydrogen, and form in particular NH3 molecules. In an alternative embodiment of the invention, the second polar molecules comprise fluorine and/or chlorine. When selecting the exchange adsorbent, one must pay attention that the second polar molecules support the desired rapid heating process and are in no way disruptive. Thus, for example, an undesired oxidizing effect of water is avoided if one selects NH3 as the second polar molecule and thus a frequently desired nitridation or a reducing effect upon the object to be processed is brought about. Depending upon the process, the second polar molecules can be NH3, O3, NO2, NO, PH3, SiH4Cl2 or weakly polar molecules such as TiCl4 or SiH4, whereby in connection with their chemical compatibility, mixtures of these gases could also be utilized. The pressure in the chamber is advantageously controlled to an overpressure or an underpressure. A sequential desorption in multiple rinsing stages can also be advantageous, whereby in each stage different polar molecules or molecule mixtures are utilized.
The present disclosure is particularly suitable for the removal of water and oxygen molecules from the processing and/or transfer chamber of a rapid heating unit for the thermal treatment of semiconductor wafers.